Minimal Martian Terraformed Atmospheres

nickname · 2007-11-27 17:49:29

Hi Rick,

Your Welcome.

I'm always shocked at how little info exists about the toxicity of c02 with plants, lots of such info about animals but not much on plants.

I guess the percentages we are talking about on Mars just don't exist on earth unless we have a local co2 volcanic event or enclosed greenhouse.
So i can understand why it's not common knowledge.

I'm not sure on the c3 or c4 groups being studded for c02 toxicity, they both have a limit in co2 % for different reasons.
A few plants can withstand 10% but not all the time.

Taking into account the lower bar pressures on a warmed Mars we might get away with 10% -15% co2 all the time, but not much beyond that.
That is something we will have to think about should we decide to import nitrogen, as the more nitrogen we add the lower the c02 toxicity % becomes just from increased Martian bar pressure.

Mosses are a little different for c02 but have pretty low tolerances for UV.
Peat moss is a good choice in bogs on a UV protected Mars with semi decent atmospheric nitrogen %.

The fungus families are nearly immune to co2, but some of the weakest for radiation doses.
Most would need a bio mass to function at all though, a few can eat rock and need no sunlight.

Cyano i think will be happy in the ponds on Mars, i can only see waves as a potential problem overdosing co2, a not very likely situation.
We probably had a similar co2 environment and iron rich water on Earth when cyano started growing, i bet earth had waves trying to add co2 and increased radiations and cyano grew ok.

nickname · 2007-11-27 18:14:52

Midoshi,

We have some pretty incompetent leaders here on earth, no reason to believe that trait wont be exported to Mars

Great fun to think about what Mars and life will need both together to be happy places.

Seems to me most of the serious problems go away with nitrogen import, but the penalties to do that are pretty big.

Good thing is we really are not rushed to bring in nitrogen.
We can do that over thousands of years.
We still have a Mars on the right path with life already started in the water as soon as we warm it.
So for the first 5,000 - 10,000 years we live indoors and go outdoors with oxygen masks.
Not such a giant penalty when the Martians contemplate the final day they put away the masks for good.

Fiddling with small changes to amounts of oxygen, c02 and nitrogen is what those Martians will be doing when Mars gets close to perfect to start planting the land.

Thanks for the link on animal c02 adaptability, going to read that right now.

qraal · 2008-01-02 06:39:19

Hi All

It's a bit of a mistake to say 35% O2 auto-ignites, as those studies used paper in over-pressurised containers. Earth in the Carboniferous had ~35% O2 and no global conflagrations are known in the fossil record.

Reality is that low pressure pure O2 can be used without those issues arising. High partial pressures enhance flammability - though still higher levels of inert components, or even fuels will eventually suppress ignition.

As for too much CO2 I reckon somatic cell gene tinkering will let us increase our tolerance levels on a reversible basis. And tricky nanotech masks might scrub the rest, if we have too much.

RickSmith · 2008-01-03 14:28:28

As for too much CO2 I reckon somatic cell gene tinkering will let us increase our tolerance levels on a reversible basis. And tricky nanotech masks might scrub the rest, if we have too much.

Hi qraal, everyone.
I've talked elsewhere about solving hard problems with Magical Nano Technology so I won't discuss it further here. But I think it will be very hard to genetically engineer people to accept high CO2 levels.

CO2 in the blood binds with the hemoglobin. When it reaches the lungs it has air on the other side of the membrane with effectively zero partial pressure for CO2. The gibbs free energy (a chemical measure of energy, entropy and probability) drives the CO2 across that barrier. If you increase the CO2 level in the lungs, not only does the CO2 in the blood 'want' to stay there more, but the CO2 in the air starts binding with the red blood cells.

Last, high CO2 concentrations decrease the blood PH that have a variety of bad effects.

I've enjoyed a number of your posts qraal, but I think you are underestimating the difficulty of dealing with CO2. One thing that I think would be useful is a cybernetic sense organ that tells people the CO2 level. Wire it up to the pain center and people will instantly know if their is a dangerous level of CO2 building up in their air.

Warm regards, Rick.

qraal · 2008-01-03 14:54:52

Hi Rick

Thanks for the nice reply. What do you think of Bob Forward's idea, from one of his novels, of a nanotech mask that filters the CO2 out directly?

I do like the artificial sense, but I was thinking more of Kim Robinson's idea of bicarbonate binding like crocodiles when I made my quip about enhanced CO2 tolerance.

RickSmith · 2008-01-03 15:34:40

Hi qraal, everyone.
Hard science fiction is held by me to some contradictory standards. If the technology or science breakthru is important to the plot I like it to be explained some how. Background breakthrus I don't expect as much explanation. Realistically if you assume science and technology increases for another 100 years, there SHOULD be all sorts of improvements and an author can't take the time to explain them all.

Science fiction often uses Magical Nano Technology to 'explain' all sorts of tough technological breakthrus with out having to discuss them in detail. That is fine for what SF does.

But in a science forum I hold higher standards. HOW is your nano-tech mask going to lower the partial pressure of CO2? See this thread:

Problems With Magical Nano-technology

In particular, in the last post I've made (so far) in this thread I give an example of a nano-tech problem where it could work because the problems with nano-tech (which most people gloss over) are addressed.

Warm regards, Rick.

Terraformer · 2008-01-04 07:54:14

Off topic, but...

It's a bit of a mistake to say 35% O2 auto-ignites, as those studies used paper in over-pressurised containers. Earth in the Carboniferous had ~35% O2 and no global conflagrations are known in the fossil record.

...how does this affect the terraforming of Titan?

mjsimon · 2008-01-07 16:03:56

Hello, I just stumbled across this forum, was fascinated, and had to weigh in, particularly in regards to the "magic nanotech wand", which also bothers me.

There are two problems with carbon dioxide in the bloodstream that have been mentioned already, displacement of O2 and lowering blood pH. I'll propose a solution that I haven't seen discussed on this topic. Forgive me if such things have been discussed in previous topics.

1: Reduce the affinity of Hemoglobin for CO2. This helps oxygen transport as reducing the affinity for CO2 increases the time that Hb will spend in its Oxygen friendly state.

2: The problem with 1 is that Hb is now poorer at removing CO2 from the bloodstream, a bad thing. This is still sort of okay, however, since so much more CO2 is present that we'll still get rid of a lot of it even though binding affinity is lower. Anyway, it might help to have extra wild-type Hb in the blood to increase our abilility to get rid of the stuff.

3: Chances are, the partially terraformed Martian atmosphere is still going to have way too much CO2 for not radically altered (ie, beyond the scope of my understanding) proteins. Therefore, we need a carbon sink in the bloodstream to keep folks alive and functioning for some amount of time in the unprotected environment. Hemoglobin again provides a possible solution. A modified form could be introduced into the bloodstream (via whatever delivery device one finds appropriate) that has a very low affinity for both oxygen and CO2. Low O2 affinity is important because we don't want it to interfere with "normal" respiration, and low CO2 affinity is important because we only want it to hold onto CO2 at very high levels, not at normal levels.

My theoretical contraption for 3 is thousands to millions of microscopic beads whose interiors have the described low affinity Hb mutant contained inside. A CO2 sensor opens or closes the beads as CO2 levels raise and lower, exposing or hiding the CO2 trapping Hb molecules when appropriate. The implementation is really just an engineering question as to what works best. I don't know the answer, but it's certainly a knowable answer.

RickSmith · 2008-01-07 22:58:02

Hi mjsimon.
Welcome to the forum! I had a bit of difficulty following your post. Is Hb a standard abbreviation in biology? Do we have any experience with successfully modifying hemoglobin or was this just theoretical?

Your final point about small spheres that act as a CO2 trap if things get dangerous. How would they discharge the CO2? One way is that after they are filled, their surface changes somehow so that they will be simply flushed from the body.

Thanks for the interesting post!

Warm regards, Rick.

mjsimon · 2008-01-08 07:48:25

Rick,

First off, my apologies, Hb is shorthand for Hemoglobin.

To answer your first question, there are known forms of Hb with higher binding affinity to O2 (fetal Hb), a mutation has also been observed that increases affinity for O2.

see http://www.pubmedcentral.nih.gov/articl … id=1220602 for info on O2 binding mutant (albiet based on the embryonic form of Hb).

I don't know of a mutation that increases CO2 binding, so that is more theoretical, but Hb is one of the best understood proteins in the human body and I'd be surprised if one couldn't be rationally designed. Failing this, designing a CO2 binding molecule based on the deoxy (high CO2 affinity) form of Hb's binding site. Again, theoretical, but pretty down to Earth as theories go.

This doesn't mean it's going to be easy, of course. Our proteins behave the way they do because it keeps us alive. Any changes are suspect, potentially throwing off the biochemical balance. A huge amount of testing would be necessary to bring this into humans.

To clarify my idea in more detail let me try and describe it better.

You have a hollow sphere that is divided into 4 quadrants with a hinge at the top of the sphere holding the quadrants together. The hinge has a CO2 sensor on it that controls whether the bead is closed (a sphere) or open (internal contents exposed). The internal surface is coated with modified Hb proteins or just CO2 binding sites described above.
At high CO2 blood concentrations, the bead opens, exposing binding sites that start binding CO2. When the blood CO2 drops low enough, the binding sites will start dropping CO2, which is then picked up by normal Hb and carried to the lungs as normal. Then the bead closes.
The important thing is that the CO2 binder has affinity for CO2 less than normal Hb (only binding excess CO2 and not stripping the blood of it). Also, the sensor needs to activate at a lower concentration of CO2 than the modified Hb binds. You don't want the beads closing with modified Hb still holding on to CO2, you want to get rid of it when you're back in normal atmosphere. This rational is for a reusable system, if you want a single use system like Rick described, you want to close the bead when CO2 is still bound.

In all honesty, a single properly designed Hb molecule would do the job, striking the correct balance between O2 and CO2 affinity to deal with increased CO2 concentration. A much more elegant, but much more difficult proposition. Another (partial) solution would be to alter the way the body buffers the blood. If you can reduce the impact dissolved CO2 has on blood pH, then you mitigate some of its toxic effects.

I hope this was clearer,

Michael

Antius · 2008-01-08 07:49:13

A minimal atmosphere of 100mb CO2 would dramatically improve the economics of living on Mars, given that it would allow non-pressurised greenhouses to be used for the growth of crops.

At 250mb, humans could live in domed habitats that were only slightly pressurised with pure oxygen. Again, this would dramatically improve the economics of living on the planet, given that the cost per square metre of habitable area would go down dramatically. Only relatively lightweight structures would be needed to provide habitable atmospheres for cities. At 250mb, the column density of the atmosphere would be 2/3rds Earth sea level, so cosmic ray dose should be eliminated. The high CO2 level would also warm the planet to comfortable temperatures.

We could actually reduce the cost of living on Mars by 99% without changing the composition of the atmosphere (ie, a higher partial pressure of CO2, but low levels of O2).

RickSmith · 2008-01-12 15:56:46

To recap: so our atmosphere might now look like:
Composition:
- CO2.....55.0 mBar
- N2..........3.36 mBar
- Ar...........0.1 mBar ?
- O2..........0.012 mBar
- H2O........0.01 mBar (rising with increasing temperature.) ?
- Various trace gases ~0.001 mBar
- C2F6.....0.00003 mBar
- C3F8.....0.000125 mBar
- C4F10...0.00001 mBar
- SF6........0.000045 mBar
- NO2.......0.00001 mBar
Total: ~58.5 mBar.

Hi everyone,
OK, the above numbers are where I had got to in Terraforming Mars' atmosphere. We had warmed the planet to out gas CO2 (further warming the planet) and then had dropped a lot of iceteroids to add N2 (and other sundry gases).

One thing that the above atmosphere mix does not take into account is the amount of time it takes for all those rocks to be moved. If it takes 200 years to get the N2 concentration up, then we have 200 years of warming and the CO2 concentration would rise higher than what I guessed above. How much it would rise is very hard to say. Likely there are huge amounts of CO2 clathrate on the planet but we won't see much of that freed until the temperature approaches 0 degrees C for at least part of the year at 40+ degrees latitude.

Also a lot of water has been dropped on the planet. This will freeze out as ice and snow. (Breaking up some dusty CC asteroids to darken the snow would be good but in the long run blowing Martian dust will dirty the snow naturally.)

I have reached the point of outright guesses here but likely the CO2 level will have risen from 100 to 150 KPa (0.1 to 0.15 bars). This will allow people to walk on Mars with out pressure suits. We have enough N2 for nitrogen fixing plants but the land is too cold for much in the way of water OR planets.

Nickname has pointed out that high CO2 concentrations are toxic to some plants. This is something I hope to find time to research more. However there are some simple plants that can be used to increase the O2 concentration so it is not a complete show stopper. We are also hurt by the high UV flux on the ground.

However, I think that we are reaching a wall. We will need more big engineering to take us to the next level (adding enough O2 to the air to reduce ultra violet at ground level). So I will assume that people keep pumping super greenhouse gases into the air and that bigger solettas are put up to warm the poles. We will assume that at 50 degrees latitude we have summer temperatures over 0 degrees C.

We now have a lot of ice melting each summer.

Martian dirt outgased a couple percent O2 when it was warmed and got wet. (The Viking experiments.) Some think this was because of native Martian life, others postulated exotic soil chemistry. (Altho no one has been able to come up with soils that mimic the effect so that hypothesis has some problems.) In any case we will get some O2 for free as soon as we wet the soil. With flowing water we should get some cyanobacteria living in pools or in lakes under a skim of ice. O2 will now be pumped in small dribs and drabs to the air.

Now UV light breaks up O2. The free O atoms combine with O2 to form ozone (O3) which block UV light. Until we get a proper ozone layer high in the atmosphere O3 will be formed near the ground. Ozone is highly reactive and will damage life, plastic domes, etc.

I have found NO data that discusses how high the O2 level must be to 'use up' all the UV high in the atmosphere. One thing to consider is that the Martian atmosphere will be deeper than Earth's air (Mars has a greater scale height). As the ozone layer builds up it will likely form a far deeper layer than Earth, originally extending down to ground level. The ozone will likely be quite dilute at ground level. (I hope!)

As the O2 level increases, more and more of the ozone will appear high in the atmosphere. The UV flux will drop on the surface and life will find things much easier, increasing the rate at which O2 is pumped into the air.

This will likely take 500 to 5,000 years. Thruout this time, more CO2 will be leaking into the air as soils warm and clathrates melt. Bacteria will be slowly freeing N2 from rock and soil and releasing it into the air. Note that our new life is not likely lowering the CO2 level very much. They draw down CO2 as they build their tissues but when they die and rot they release it back into the air. To lower the CO2 level we must BURY the CO2. That is the last big task for terraformers.

So at the end of stage 3, (perhaps 3,000 to 5,000 years after the first mirrors went over the poles) our atmosphere might look like:

Composition:
- CO2...300.0 mBar (or more?)
- N2........15.0 mBar
- Ar...........0.1 mBar ?
- O2..........1.0 mBar
- H2O........1.0 mBar

- Various trace gases ~0.01 mBar

- CF4.......0.0002 mBar
- C2F6.....0.0004 mBar
- C3F8.....0.0015 mBar
- C4F10....0.0001 mBar
- SF6........0.003 mBar
- NO2.......0.0001 mBar

Total: ~317.2 mBar.

(There is a LOT of guessing in the above.)

At this stage things are looking fairly bright. Plants can start spreading naturally to large areas of the planet so the O2 level will likely start rising more quickly. There is enough O2 for microscopic 'animals' and we are getting close to where crawling insects can live (except of course that the high CO2 level would smother them). The ozone will act as a cold trap preserving the H2O on the planet. The planet is wet enough that the super fine dust (fines) will start cementing together into less dangerous dust. (The down side of this is that the snow will stay white longer which will cool the planet.) The air will have enough O2 in it that simple low tech compressors will allow people to chemically separate enough O2 to live which will lower the cost of life support significantly.

Gradually, CO2 will be drawn down and buried. (Peat moss anyone?) but to get a breathable atmosphere from this point, naturally, will take an estimated 100,000 years. However, humans can deliberately bury carbon greatly speeding up the formation of a breathable mix of gases.

Anyway, these essays show my best guess on the minimum effort and duration to get us to a 'stage 3' atmosphere. I see this taking an intensive 200 year effort at a start and another intensive effort around the 200 year mark to raise the temperature another 20 to 30 C once we have a reasonable amount of N2. Thruout this period, people will have to keep adding super green house gases to maintain the warmth. (That is why I like adding a lot of CF4 to the air. It lasts so long that people might have time to recover from a period of relatively low tech with out the planet freezing on them.)

Note that this terraforming story does not require any scientific breakthrus and only some modest technological ones (to build the large space mirrors). With scientific breakthrus, (e.g. UV resistant plants), it would only speed up the process. Larger engineering efforts (e.g. many fusion bombs to melt water and free N2 and CO2 from the ground.) would also speed up this time line.

Warm regards, Rick.

MarsRefresh · 2008-01-13 17:44:46

Good stuff Rick.

When would large bodies of liquid water become stable on the surface? Say we did everything possible to retain snow melt in Schiaperelli (461 km in d) and Huygens (456 km in d) craters (equatorial Mars) to form shallow seas to support diatoms and phytoplankton. These can cycle large amounts of CO2 and O2 (as we discussed with global warming) creating a more dynamic atmosphere. And we sure wouldn't need to fertilize the water with iron.

RickSmith · 2008-01-14 22:17:34

When would large bodies of liquid water become stable on the surface? .... And we sure wouldn't need to fertilize the water with iron.

Hi MarsRefresh, everyone.
I smiled out loud over the iron fertilizer thing. No, I can't see iron being the limiting element in plankton growth.

The question of when water will become stable depends on if you count water with ice on top of it. Also the salinity can lower the melting point of ice of course. Water is very dark so it absorbs heat well.

Currently Mars is so cold that super saturated brines last for a surprising amount of time (minutes) before they evaporate. If we increased the pressure 4 fold, we should be able to get stable hypersaline brines in the warmer equatorial regions. EDIT: I found that hypersaline brines can lower the freezing point of water by 60 C. 30 degree drops are quite easy to achieve.

As we add pressure and warm the planet you end up in a race. The higher pressure makes water more resistant to evaporation. The increased temperature makes it more likely to evaporate. The kicker is when a significant amount of water vapor is in the air, that depresses evaporation and makes liquid water much more likely.

If we can get the pressure up to 100 mBar, then the freezing point of water will be ~0 C and the boiling point is ~60 C. (It will still evaporate in the dry atmosphere.)

So in answer to your question, it won't take much to make local brines stable on the equator. But for lakes and seas, we want temperatures a bit over zero and pressures around half a bar and up.

EDIT:
The link below from NASA says that liquid water can exist on about 30% of Mars' surface now. (It won't boil but will evaporate since the air is very dry.) However the water has to be at just the right temperature. If it is slightly colder it freezes. If it is bit hotter it boils. (Dissolved salts will increase this temperature range a bit.) However, if we increase the air pressure and temperature a bit, the temperature range where liquid water is stable is much higher. Note the phase diagram in this article shows how the range between ice and vapor expands as the pressure goes up.

Making A Splash on Mars

Warm regards, Rick.

MarsRefresh · 2008-01-15 18:42:17

When would large bodies of liquid water become stable on the surface? .... And we sure wouldn't need to fertilize the water with iron.
Hi MarsRefresh, everyone.
I smiled out loud over the iron fertilizer thing. No, I can't see iron being the limiting element in plankton growth.
The question of when water will become stable depends on if you count water with ice on top of it. Also the salinity can lower the melting point of ice of course. Water is very dark so it absorbs heat well.
Currently Mars is so cold that super saturated brines last for a surprising amount of time (minutes) before they evaporate. If we increased the pressure 4 fold, we should be able to get stable hypersaline brines in the warmer equatorial regions.
As we add pressure and warm the planet you end up in a race. The higher pressure makes water more resistant to evaporation. The increased temperature makes it more likely to evaporate. The kicker is when a significant amount of water vapor is in the air, that depresses evaporation and makes liquid water much more likely.
So in answer to your question, it won't take much to make local brines stable on the equator. But for lakes and seas, we want temperatures a bit over zero and pressures around half a bar and up.
I don't have time right now to give more details. Check back later and I'll give harder numbers.
Warm regards, Rick.

A good idea dies hard.

So the 1/2 bar pressure will require thousands of years in the above scenario. Obviously that's a long time. Have you detailed how much/many iceteroids your scenario has introduced?

RickSmith · 2008-01-15 21:16:24

A good idea dies hard.
So the 1/2 bar pressure will require thousands of years in the above scenario. Obviously that's a long time. Have you detailed how much/many iceteroids your scenario has introduced?

Now we need to increase the current N2 pressure by about 28 times. I am assuming that half of this comes by H-Bombs in deep rock deposits. I am assuming that for every tonne of nitrogen brought by iceteroid an extra tonne of nitrates are volatilized by the impact. So we would need to increase Mars' nitrogen level by 7 times via direct importation. (This would be 240 impacts of the 2.6 km bodies described above.)

This is from the post near the top of this thread where I'm trying to increase the N2 partial pressure to the point where nitrogen fixing bacteria have enough N2 in the air to fix.

Note that if you halve the radius, you increase by ~8 times the number of asteroids that you need to move. (Of course each asteroid is 8 times easier to move...) Large impacts blow away bits of atmosphere, where as small impacts blow away zero to an insignificant amount of air. So I generally suggest we move lots of smaller bodies than a couple big ones.

Under my "slow but steady" terraforming story above, I suggest it will take several centuries to get the partial pressure of CO2 up to 300 mBar. But this is based on what the CO2 reserve is like, which is simply unknown. My estimates were quite conservative. If there is more CO2 than the minimum, we might reach 500 mBar in only 3 or 4 centuries.

However, even at 200 mBar, we should be able to enjoy lakes that freeze during winter. Many (most?) species of cyanobacteria are not killed by a winter freeze so we should be able to get a biosphere started in small areas quite early.

Another assumption I make is that we make a push to warm Mars by 10 to 20 degrees and then seriously don't try to warm it more until we have a larger pressure of nitrogen in the air. But this is an artificial delay so that I can talk more clearly about what happens at each stage. (It also assumes that some administrations basically ignore terraforming for a while.) There is no reason to think that after people get Mars 20 degrees warmer they will slow down. If they keep pushing and get it another 30 or 50 degrees C warmer, then everything will happen much faster.

A lot of this delay is how long does it take the heat on the surface to work its way down into the subsoil. If the surface is a lot warmer, the wave of heat moves more quickly, which will drive the CO2 out of the soil that much faster.

In summary, I assume in this series of essays that we have a slow and steady push for terraforming. People do not aim for the final goal that is a long way away. Instead they say, "forget the O2, I just want to be able to dump pressure suits. Let's thicken the air some.". The point is that it is hard for a government to aim for a goal that is 1,000+ years away. But several subgoals exist that could improve the planet in significantly smaller time frames, which make steady progress on terraforming more likely. (And Mars is so cold that increasing the temperature just a degree or three will be popular politically for a long time.)

Warm regards, Rick.

qraal · 2008-01-17 05:56:32

Hi All

Water Boiling Point with Pressure
0.006112 bar, 0.01 C = Triple Point
0.01 bar, 7 C
0.02 bar, 17.5 C
0.03 bar, 24.1 C
0.04 bar, 29.0 C
0.05 bar, 32.9 C
0.06 bar, 36.2 C
0.07 bar, 39.0 C
0.08 bar, 41.5 C
0.09 bar, 43.8 C
0.1 bar, 45.8 C
0.2 bar, 60.1 C
0.3 bar, 69.1 C
0.4 bar, 75.9 C
0.5 bar, 81.3 C

... as you can see for expected temperature ranges (<15 C) the partial pressure of water over a body of water will be pretty low. Once it evaporates what happens to it? If it's warmer than its surroundings then the vapour will rise, eventually hitting the Lifting Condensation Level, thus forming clouds and, of course, clouds eventually precipitate. If it's as rain, the water will end up back in the body of water it came from, or some new body, but if it falls as non-seasonal snow (say on a high mountain glacier) then we might not see it again.

Vapour pressure over Ice...

0.01 C, 0.006112 bar
-10.0 C, 0.002598 bar
-20.0 C, 0.001038 bar
-30.0 C, 0.0003809 bar
-40.0 C, 0.0001288 bar

...thus why the -40 C air of Everest's summit is so painfully dry. Also why exposed ice is unstable in the open vacuum - things have to get really cold for ice to last over the age of the solar system, or else it needs to be coated in dust and tholins (think asphalt.) It's also why the water isn't coming back from cold glaciers if we don't control the mountain and polar temperatures on Mars.

Just a few more facts to guide discussion. Pressures are a bit lower over salty water too.

MarsRefresh · 2008-01-18 22:10:25

However, even at 200 mBar, we should be able to enjoy lakes that freeze during winter. Many (most?) species of cyanobacteria are not killed by a winter freeze so we should be able to get a biosphere started in small areas quite early.

Excellent. I wonder how much ice thickness affects life in the photic zone. Obviously a relatively thin ice layer transmits some light to the water below. At what thickness does ice reduce the photic zone to zero? But given that phytoplankton survive in the Arctic Ocean that freezes over and goes many months with little light suggests that such a Martian environment might be less harsh. Global warming concerns are pumping money into Arctic research.

MarsRefresh wrote:
A good idea dies hard. Very Happy
So the 1/2 bar pressure will require thousands of years in the above scenario. Obviously that's a long time. Have you detailed how much/many iceteroids your scenario has introduced?

Rick wrote:
Now we need to increase the current N2 pressure by about 28 times. I am assuming that half of this comes by H-Bombs in deep rock deposits. I am assuming that for every tonne of nitrogen brought by iceteroid an extra tonne of nitrates are volatilized by the impact. So we would need to increase Mars' nitrogen level by 7 times via direct importation. (This would be 240 impacts of the 2.6 km bodies described above.)

This is from the post near the top of this thread where I'm trying to increase the N2 partial pressure to the point where nitrogen fixing bacteria have enough N2 in the air to fix.
Note that if you halve the radius, you increase by ~8 times the number of asteroids that you need to move. (Of course each asteroid is 8 times easier to move...) Large impacts blow away bits of atmosphere, where as small impacts blow away zero to an insignificant amount of air. So I generally suggest we move lots of smaller bodies than a couple big ones.

Thanks. It makes sense that large impactors would be defeating the purpose. However, as the atmosphere thickens the prospects of inserting a larger object with a highly elliptical orbit to "aerobrake" into the upper portion of a 200 mb atmosphere could potentially bleed off a lot of material before the orbit decayed into an impact. The MRO clipped the upper atmosphere repeatedly to slowly move into a smaller orbit. Obviously that's a whole different scale than we are talking about here.

MarsRefresh · 2008-01-18 22:22:32

qraal wrote:

If it's as rain, the water will end up back in the body of water it came from, or some new body, but if it falls as non-seasonal snow (say on a high mountain glacier) then we might not see it again.

Good point. "The Alpine Glaciers of Tharsis are lovely this time of year..."
Although the possibility of glacier-fed rivers is pretty neat. Obviously if ice is accumulating above a given altitude then a transitional layer of seasonal freeze/thaw would exist below the permanent glacier and stream systems would develop.

Also, the gentle profile of the great mountains would allow for thicker glacial accumulations and slower movement - a recipe for a lot of water "wasted" in alpine glaciers. And then there's the southern highlands...

Midoshi · 2008-02-08 16:50:57

I'm making this (admittedly massive) post in an attempt to correct some stuff I've seen on these forums and offer some new information about the requirements for a breathable atmosphere. The overall goal is to present an upper limit to tolerable CO2 levels (jump to the end if you just want to know), but I'd like to start with two general points:

*************************************************************

Saying that humans can't live with more than [insert safety data sheet value] mbar of CO2 because of tocixity is like saying people can't live in the Andes because of lack of O2.
Occupational Safety and Health Administration guidelines dictate that the Permissible Exposure Limit for CO2 is 0.5%, and the level Immediately Dangerous to Life and Health is 5% (both assume a total pressure of 1 atm, i.e. sea level). At these levels shortness of breath, headache, and dizziness are reported. Similar symptoms are associated with altitude sickness, which begins to occur when someone from sea level ventures up to altitudes of 1500-3500 m. Contrast this with the fact that the city of Potosi in Bolivia is located at 4000 m and has a population of over 130,000 according to the INE 2001 census. The point is that the acclimation capabilities of humans (and other organisms) should not be underestimated.
Sources:
High Altitude Illness, Ivan Schatz, M.D., Western University of Health Sciences
www.californiamountaineer.com/HIGH%20ALTITUDE%20ILLNESS.pdf
Ansul Incorporated Carbon Dioxide Material Safety Sheet
www.ansul.com/AnsulGetDoc.asp?FileID=13400

Breathing 5% CO2 on Earth is not the same as breathing 5% CO2 on Mars.
This is a common misconception I've noticed on these forums, and it really needs to be cleared up. The truth is that respiration in organisms depends only on partial pressure of gases. Going by just percentages will get you in trouble. Let's do an example. Say that Bob has acclimated to breathing 5% CO2 on Earth at sea level. What this really means is that he has acclimated to breathing (5% CO2)*(1 atm total) = 50 mbar CO2. Now let's put him in a terraformed Mars atmosphere of 250 mbar. The amount of CO2 Bob can handle on Mars is the same as on Earth: 50 mbar CO2. But when you convert to percentages, that's (50 mbar CO2)/(250 mbar total) = 20% CO2. I hope this simple example gets the point across that taking straight gas percentages can be inaccurate when considering the breathability of a terraformed Martian atmospshere.

*************************************************************

So, how much CO2 can we take? Here are the key effects to consider:

#1) CO2 replaces O2 on hemoglobin, thus depriving you of oxygen
#2) CO2 causes acidosis, i.e. a blood pH imbalance
#3) CO2 causes an inert gas narcosis, similar to nitrogen in scuba diving

#1: INHIBITION OF O2-HEMOGLOBIN BONDING

The first effect, inhibition of O2-hemoglobin bonding, turns out to be negligible:

Only a small fraction of the CO2 in your blood is transported by hemoglobin.
The vast majority (~90%) of the CO2 in blood is transported by bicarbonates.
Source: Clinical Anesthesiology, M. J. Murray, G. E. Morgan, and M. S. Mikhail, New York: McGraw-Hill (2002)
http://books.google.com/books?id=Z8BFSS9tsgwC

Blood CO2 levels have only a small effect on O2 binding to hemoglobin.
To illustrate: Like elevated CO2 levels, raising body temperature negatively impacts O2-hemoglobin binding. Normal CO2 arterial pressure is 40 mmHg. Increasing this over seven times to 300 mmHg (400 mbar) has as much effect on O2-hemoglobin binding as raising core body temperature to 102.6°F, which is only a moderate fever. Fevers aren't fun, but no one dies from respiratory failure due to inadequate O2-hemoglobin bonding.
For more information, play with this applet: http://www.ventworld.com/resources/oxyd … disso.html

#2: RESPIRATORY ACIDOSIS

The second effect, acidosis, is the major cause of the toxicity typically associated with CO2. But what seems not to be so widely known is that it can be overcome through acclimation over a few days, much like altitude sickness. As I've noted in a previous post, this is because the carbonic acid formed in the blood by the CO2 is neutralized by the kidneys retaining bicarbonates ions. Just to reiterate, humans have been adapted without significant complications to 4% CO2, Rhesus monkeys to 6% CO2, and sheep to 12% CO2.

Only in the experiment with sheep was some sort of limit of acclimation reached. The study was reported on in at least two papers from the early 70s by Hoover et al., who detailed the nutritional and physiological responses. Negative effects began around 8% CO2, but were tolerable up till 12% CO2. Eventually serious degradation occured at 16% CO2, with the sheep becoming lethargic, beginning to drool, and ceasing to eat. Subsequently, the experiment was stopped. But the question is, what caused these symptoms? There does not seem to be any obvious reason why the bicarbonate buffer of the body would fail at that level.

#3: INERT GAS NARCOSIS

The answer is that the third effect, inert gas narcosis, is coming into play. It turns out that every gas has some pressure at which breathing it will cause symptoms similar to being drunk. At even higher pressures it will act as an anesthetic. These effects are thought to be due to the gas diffusing across cell membranes and interfering with neural signals. Thus, the narcotic potency of a gas would be expected to be related to its solubility in lipids and oils. This is confirmed by experiment. The graph below depicts the points at which a number of gases cause inability to feel pain in a standardized test:

So chloroform is a good anesthetic because it is extremely oil soluble and will knock you out at only trace pressures, while helium is almost impossible to "overdose" on in terms of narcotic effects and is thus used in deep diving where you have to breathe high pressure gases. Nitrogen isn't quite as good as helium, and so its narcotic effects can be significant when diving at relatively shallow depths. For nitrogen a biological response, not significantly impairing, can occur as shallow as 60 ft of sea water, or 1.5 atm of pressure, which for breathing air would be 1.2 atm N2. The safety guideline limit is 100 ft of sea water, or about 2.4 atm N2. Deeper than this and serious impairment of judgement similar to drunkeness can occur.

Now look at where carbon dioxide is on the graph. It's much more narcotic than one would expect based on the lipid solubility theory. This increased potency is due to acidosis, the second biological effect of CO2 on our list. But we know that the effects of acidosis can be compensated for by the kidneys. This means that, given time to acclimate, the narcotic potency of CO2 will decrease, and it will move up on the graph to join the company of nitrous oxide (laughing gas) and xenon. Thus, the theory of inert gas narcosis provides us with the real limit to breathable CO2 levels.

So what exactly is this limit? According to lipid solubility theory CO2 should be 20 times more potent than N2. This suggests that biological response will begin at about (1.4 atm N2)/20 = 70 mbar CO2, or 7% CO2 at sea level, and the safety limit will be (2.4 atm N2)/20 = 120 mbar CO2, or 12% CO2 at sea level. I was quite happy when I saw this, because it agrees well with the study on sheep that I mentioned before.

Now I want to note that there's significant "wiggle room" in these calculations. For example, it is difficult to evaluate the narcotic contribution of O2 at high pressure when looking at diving, but some people think that it's similar to N2. If we accept that and redo the calculations, we find a biological reaction threshold of about 90 mbar CO2 (9% CO2) and a safe limit of 150 mbar (15% CO2). These are a bit different from the numbers we got assuming just N2 was narcotic, but they're still consistent with the sheep experiment. Also, while it's true that sheep and humans have similar inert gas narcosis reactions, it turns out that humans are 8% more "durable", i.e. the sheep study pressures have to be bumped up 8% to get a correct pressure/response correlation for humans. Finally, and perhaps more intriguing, it seems that there may actually be the possibility of acclimation to inert gas narcosis. Some frequent divers are capable of operating safely at depths down to 180-220 ft, which, depending on whether you try to include O2 narcosis or not, is equivalent to between 220-340 mbar CO2, or 22-34% CO2 at sea level. This is somewhat speculative though.

Ultimately, we can state with confidence a conservative lower estimate of 120 mbar for the limit of safe CO2 partial pressure. This raises the possibility that CO2 might actually be used as a significant buffer gas in terraformation.

References:

Extreme Hypercapnia in Humans

A case of extreme hypercapnia (Urwin et al. 2004)
Extreme Hypercapnia in a Fully Alert Patient (Meissner & Franklin 1992)

Effects of Hypercapnia

Bone Loss in Patients with Untreated Chronic Obstructive Pulmonary Disease Is Associated with Hypercapnia (Dimai et al. 2001)
Structural basis of hypoxic pulmonary hypertension; the modifying effect of chronic hypercapnia (Howell et al. 2004)
Circadian pattern of ventilation during acute and chronic hypercapnia in conscious adult rats (Seifert & Mortola 2002)
Hypercapnia Does Not Affect Functional Residual Capacity Enlargement Induced by Chronic Hypoxia (Maxova & Vizek 2002)
A Pharmacologic Study on CO2 Responsiveness of Intracranial Pressure in Rats With Chronic Hypercapnia (Kondo et al. 1999)
Cerebral Blood Flow Autoregulation and Graded Hypercapnia (Raichle and Stone 1971)
Chronic hypercapnia resets CO2 sensitivity of avian intrapulmonary chemoreceptors (Rebout and Hempleman 1999)
Chronic Hypercapnia Stimulates Proximal Bicarbonate Reabsorption in the Rat (Cogan 1984)
Effects of acute and chronic hypercapnia on oxygen tolerance in rats (Clark 1981)
Mechanisms of Adaptation to Chronic Respiratory Acidosis in the Rabbit Proximal Tubule (Krapf 1989)
Size and Composition Changes in Diaphragmatic Fibers in Rats Exposed to Chronic Hypercapnia (Kumagai et al. 2001)
The Effect of Prolonged Experimental Hypereapnia on the Brain (Matakas et al. 1978)
The Influence of Graded Degrees of Chronic Hypercapnia on the Acute Carbon Dioxide Titration Curve (Goldstein et al. 1971)
Ventilatory responses to acute and chronic hypoxic hypercapnia in the ground squirrel (Webb & Milsom 1994)
Ventilatory responses to hypercapnia and hypoxia following chronic hypercapnia in the rat (Kondo et al. 2000)
The brain in extreme respiratory acidosis (Paljärvi et al. 1982)

Effects of Hypercapnia + Hypoxia

Carbon Dioxide-Oxgen Interactions in Extension of Tolerance to Acute Hypoxia (Lambertsen et al. 2001)
Cardioprotective Effect of Chronic Hypoxia is Blunted by Concomitant Hypercapnia (Neckar et al. 2003)
Chronic hypercapnia inhibits hypoxic pulmonary vascular remodeling (Ooi et al. 2000)
Hypercapnia Does Not Affect Functional Residual Capacity Enlargement Induced by Chronic Hypoxia (Maxova et al. 2002)
Renal compensation to chronic hypoxic hypercapnia (de Seigneux et al. 2007)
Respiratory adaptation to chronic hypercapnia in newborn rats (Rezzonico et al. 1989)
Therapeutic hypercapnia prevents chronic hypoxia-induced pulmonary hypertension in the newborn rat (Kantores et al. 2006)
Vascular Changes in the Rat Brain during Chronic Hypoxia in the Presence and Absence of Hypercapnia (Miyamoto et al. 2005)
Ventilatory responses of hamsters and rats to hypoxia and hypercapnia (Walker et al. 1955)
Ventilatory Acclimatization to High Altitude Is Prevented by CO2 Breathing (Cruz et al. 1979)

Inert Gas Narcosis

Effect of habituation to subanesthetic N2 or N2O levels on pressure and anesthesia tolerance (Brauer et al. 1987)
Effects of CO2 and N2 partial pressures on cognitive and psychomotor performance (Fothergill et al. 1991)
Narcotic effects of nitrous oxide and compressed air on memory and auditory perception (Fowler et al. 1980)
"NOAA Diving Manual: Diving for Science and Technology" U.S. Department of Commerce, DIANE Publishing (1994), p 3-20. Section 3.2.3.5 Inert Gas Narcosis
http://books.google.com/books?id=MV55Xe … 0788102311
(I don't know why Google Book Search thinks this is a book on the history of the coal industry in the USA...it isn't)
Effects of epidural and intravenous buprenorphine on halothane minimum alveolar anesthetic concentration and hemodynamic responses (Inagaki & Kuzukawa 1997)
Fetal Anesthetic Requirement (MAC) for Halothane (Gregory et al. 1983)
"Shnider and Levinson's Anesthesia for Obstetrics" Samuel C. Hughes, Gershon Levinson, Mark A. Rosen, Lippincott Williams & Wilkins (2002)

The (Infamous) Sheep Study

Effects of High Carbon Dioxide Levels on Nutrition of Sheep (Knowlton et al.)
Ovine Nutritional Responses to Elevated Ambient Carbon Dioxide (Hoover et al. 1971)
Ovine physiological responses to elevated ambient carbon dioxide (Hoover et al. 1970)

Miscellaneous

Neuronal sensitivity to hyperoxia, hypercapnia, and inert gases at hyperbaric pressures (Dean et al. 2003)
Alveolar-arterial P_CO2, difference during rebreathing in patients with chronic hypercapnia (McEnvoy et al. 1974)
Anthropometric and Other Factors Affecting Respiratory Responses to Carbon Dioxide in New Guineans (Patrick & Cotes 1974)
Negative arterial-mixed expired P_CO2 gradient during acute and chronic hypercapnia (Jennings & Chen 1975)
Summary of Data on Carbon Dioxide (Law firm of Covington & Burling 1986)
The carbon dioxide capacity of the human body (Adolph et al. 1928)
The Effect of Increased Ambient CO2 on Arterial CO2 Tension, CO2 Content and pH in Rainbow Trout (Cameron & Randall)
Tolerance of the Dog Heart to Carbon Dioxide (Brown & Miller 1952)

Websites

The Interactive Oxyhemoglobin Dissociation Curve
http://www.ventworld.com/resources/oxydisso/dissoc.html
Respiratory Acidosis, by Margaret Priestly
http://www.emedicine.com/PED/topic16.htm
Extending The Envelope: A Primer On Self-Contained Diving Technology
http://www.cisatlantic.com/trimix/AQUAc … Diving.htm
SDUA Standard Gas Mixes
http://www.sduadivers.com/resources/200 … gas-mixes/
Exotic Diving Gases
http://www.techdiver.ws/exotic_gases.shtml
Carbon Dioxide, Narcosis, and Diving
http://www.livingseas.com.sg/articles/a … rcosis.htm
Breathing Control in Chronic Hypercapnia
http://www.rtmagazine.com/issues/articl … -06_12.asp

qraal · 2008-02-08 19:52:31

An excellent mini-report there for us to ponder. Does make the situation somewhat happier than we were led to believe - and I've no doubt that medical technology could improve matters if we were willing to push the boundaries even further. Consider the bicarbonate handling abilities of crocodilians, for example.

Good point too about partial pressures versus percentages. I think a similar misunderstanding confuses people about oxygen levels and flammability.

So could our Martian colonists adapt to a 50:50 mix of CO2/O2 at 240 mbar? I would tentatively say "yes", so long as it wasn't excessively cold. What's the main cause of the "Death Zone" that mountaineers face when scaling Everest? Low pressure, low O2 or cold conditions? Didn't Tim McCartney Snape scale Everest without supplemental O2?

Midoshi · 2008-02-08 23:53:30

So could our Martian colonists adapt to a 50:50 mix of CO2/O2 at 240 mbar? I would tentatively say "yes", so long as it wasn't excessively cold.

You remind me of another "happy" point: elevated CO2 levels have been experimentally shown to relieve many of the physiological symptoms caused by long term exposure to low O2 levels.

In a study by Kantores et al. in 2006, baby rats were exposed to combinations of normal and low O2 levels at normal and high CO2 levels. Rats that had been adapted to breathing 13% O2 and normal CO2 experienced a weight loss of 19%, a 47% drop in blood O2 levels, and a 21% increase in hematocrit levels (red blood cell count) compared to control on 21% O2 and normal CO2. On the other hand, rats adapted to breathing 13% O2 and 10% CO2 only experienced a 9% weight loss, and no statistical change in blood O2 or hematocrit levels compared to control. That's really something!

qraal · 2008-02-09 01:55:21

I'm quite fond of Rattus norvegicus having kept a few as pets - sadly they expired in a particularly nasty summer we had a few years ago in Australia. Rat studies are gainful employment for the little fellas and that particular study is fascinating - perhaps Martian-born colonists will happily handle what their parents couldn't without aid.

I've just completed a numerical model of different atmospheres on Ceres. I'll post some results in the Ceres topic.

MarsRefresh · 2008-02-09 14:54:35

Midoshi wrote:

Ultimately, we can state with confidence a conservative lower estimate of 120 mbar for the limit of safe CO2 partial pressure. This raises the possibility that CO2 might actually be used as a significant buffer gas in terraformation.

This is quite encouraging. The implications for life support systems are profound as well. The cumbersome separation of elevated-CO2 greenhouses with the low-CO2 habitats is nullified, eliminating the need for connecting airlocks. And the fresh smell of growing plants can waft into the living areas. I appreciate any idea that simplifies surface habitats.

RickSmith · 2008-02-09 19:46:24

I'm making this (admittedly massive) post...
Ultimately, we can state with confidence a conservative lower estimate of 120 mbar for the limit of safe CO2 partial pressure. This raises the possibility that CO2 might actually be used as a significant buffer gas in terraformation.

Hi Midoshi,
Thanks for your research! This is exactly the sort of thing that I like to see in the forum.

So to be clear, you are suggesting that a mixture of gases like:

CO2: ....... 120 mbar.
O2: ......... 200 mbar.
N2 .............. 5 mbar. (Plants can now fix nitrogen.)
Ar ............... 1 mbar.

could be breathed in both greenhouses and the main residential areas?

Very warm regards, Rick.

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